The invention refers to a cooling element for a melting furnace with at least one cooling pipe for the passage of a cooling agent, and a support element to which the cooling pipe is fastened and wherein the at least one cooling pipe is welded together with a cover plate.
Melting furnaces usually consist of a container made from steel. For protection of the steel container, water cooled elements are fixed interiorly at the wall of the container. The space between the water-cooled elements are filled with fireproof material, for example, with pre-formed stones or also with a cast mass. The surface in front of the cooling elements is also covered in this manner.
The prior art of water-cooled cooling elements are roughly categorized into two alternatives. On the one hand, there are flat cooling elements, which essentially cover the complete inner wall of the furnace. These cooling elements are usually from copper and consist of a hot forged micro structure and are deep-bored for the passage of cooling water. Elements of grey-cast iron with pipes cast therein are also known. Cooling elements of this construction type are commonly referred to as stave coolers. (DE 29 07 511 C2).
On the other hand, there are special cooling elements that are also referred to a cooling boxes. Such cooling boxes are usually produced from copper mold casting (sand casting). They do not cover the furnace wall completely, only partially. They are pushed through a mostly rectangular or oval opening from the exterior into the furnace shell, from which they can be pulled out again from the outside in case of a necessary repair. For this purpose, these elements usually taper trapezoidally toward the furnace interior (DE 40 35 894 C1, WO 2010/128197 A1). In comparison thereto, stave coolers can only be constructed in the furnace interior, thus requiring a stoppage of the furnace.
The cooling elements that are installed from exterior are usually provided with one or two cooling channels that extend independent of each other. The cooling elements are welded into the furnace tank in a gastight manner. Since copper and steel can be welded together only with great effort, the copper elements are provided with a steel cuff in the area of the wall opening. Alternatively, an end plate can be provided. For example, a mounting lug can be welded to the end plate in order to simplify pulling the element out from the furnace wall.
Cast copper cooling elements which cannot be any longer subject to hot forming because of operational condition, due to their course grain structure, are susceptible to cracking at thermic cycling. This can lead to water emission into the melting furnace. The defective circulation must be halted and the defective element removed on short notice. A further disadvantage when utilizing cast copper cooling elements is the occurrence of shrinkage cavities in the sand casting process.
For the foregoing reasons, in the following known prior art, the copper portion of the cooling element is produced from hot forged micro structure.
DE 40 35 894 C1 describes a cooling element that consists of one or more bent pipes where the pipes are explosively welded together with a bottom and a cover plate. In this process, the pipe and the cover plate are shortly pressed together under high pressure such that the components fuse with each other at their grain boundaries.
WO 2010/128197 A1 describes an embodiment of a cooling elements from cooling pipes without a bottom and a cover plate. The special feature of this embodiment is that, in order to simplify the construction, the cooling pipes are trapezoidally formed, at least in vertical direction. The area around the pipe bottom is filled with fireproof materials. This has however the disadvantage that the heat transfer resistance is relatively high. As compared to the cooling element of DE 40 35 894 C1, only the surface has a low heat transfer resistance, however not the interior area filled with the fireproof mass. That has a considerable lower conductivity than the copper portion and is thus unable to take on the cooling function. The main task for the cooling elements, to protect the furnace shell from the heat radiation of the melting process, is carried out in only unsatisfactory manner.
Even the example described in DE 40 35 984 C1 of a cooling box exhibits disadvantages since the explosive joining of the cover plate with the cooling pipes, no fusion takes place and the heat transfer is thus negatively affected.
Starting from there, the object of the present invention is to avoid the foregoing disadvantages and to provide a cooling element where the heat transfer resistance is reduced. Furthermore, a process for the production of such a cooling element is provided.
According to one aspect of the invention, the object is solved with a cooling element having at least one cooling pipe for passage of a coolant, and a support element at which the at least one cooling element is fixed, wherein the at least one cooling element is welded together with the at least one cover plate, wherein the at least one cooling pipe is provided with at least one bead extending in longitudinal direction of the at least one cooling pipe which is welded together with the at least one cover plate.
According to another aspect of the invention, the object is solved by a process in which at least one cooling pipe is produced from a bar which exhibits in a cross section at least one bead along the longitudinal direction of the bar, wherein a channel for a coolant extends in longitudinal direction is produced through boring.
Advantageous developments of the invention are subject of the respective dependent claims.
The cooling element according to the present invention for a melting furnace especially a blast furnace includes at least one cooling pipe with a cooling agent channel for passing a cooling agent. The cooling agent is usually water. The cooling element further includes a support element at which the at least one cooling pipe is fastened. In addition, the cooling pipe is welded together with at least one cover plate.
In accordance with the present invention, the at least one cooling pipe has a bead extending in longitudinal direction with which the at least one cover plate is welded together. The cooling pipe has a special shape profile which permits welding the cover plate together with the cooling pipe in a special manner. Welding the cover plate to the cooling pipe results in retaining the micro structure in the area of the pipe wall of the cooling pipe. There is no weakening of the material in the area of the pipe wall due to the shift of the heat affected zone of the welding process.
In addition, the welding seam that results from the welding process can be made more durable and more secure at an even surface of the bead as compared to the rounded surface of the pipe.
The technical design of the cooling element according to the present invention thus attains an optimization of the production process in that an explosive welding can be foregone.
Welding according to the present invention is fusion welding whereby the two components to be welded together are joined by melting in the area of the welding seam, optionally in the presence of a welding material.
If the cooling pipe exhibits has only a single bead, it means that there is only a single thickening extending in longitudinal direction of the cooling pipe, wherein the thickening in form of a bead has the exclusive function to serve as welding partner for the cover plate.
Within the framework of the invention, the cooling pipe may also have two beads such that cover plates disposed opposite each other can be welded with the beads. The beads are thus disposed facing each other.
In a preferred variant, the cover plate is from copper or a copper alloy so that the welding process is not based on entirely different materials such as the pairing of copper-steel. Thus, in accordance with the present invention cooling pipes from copper or a copper alloy with cover plates from copper or copper material are welded together.
A further advantage of the cooling element according to the present invention is that not only the cover plate is involved in the heat transfer but also the bead which abuts the respective cover plate. The bead also serves to enlarge the surface of the cooling element that participates in the heat transfer.
Within the frame work of the present invention the at least one cover plate may be welded together with the bead of an outer cooling pipe and spanning across an inner cooling pipe adjacent to the outer cooling pipe. This means that the cooling element includes at least two cooling pipes, namely an outer and at least an inner cooling pipe. The inner cooling pipe contributes additionally to cooling the cover plate, so that the total cooling output is increased.
Preferably, the inner cooling pipe also has a bead so that the cover plate is constructed in two pieces. A first part of the cover plate is being welded between the two beads substantially extending parallel to each other of the inner and other cooling pipes. An inner part of the cover plate is welded exclusively with the bead of the inner pipe. In that case the bead of the inner pipe does not span across the cover plate, but projects between the adjoining first and second parts of the cover plate, such that the bead is directly involved with the heat transfer and again contributes to the enlargement of the surface of the cooling element. The heat will be introduced directly into the welded cover plate via the welding seams. The welding seams also enlarge the outer surface of the cooling element and contribute to the heat transfer.
It is particularly advantageous if the at least one bead is formed in substantially trapezoidal shape. Trapezoidal in this context means that the bead includes two flanks that are arranged at an angle to each other and that preferably merge tangentially into the rounded outer surface of the cooling pipe. The two flanks though do not meet into a point, but section an upper, or, in reference to the front surface, an outer front surface, of a trapeze. The broader base of the trapeze is formed by the rounded pipe wall. The shorter, outer front surface of the trapeze is located after the welding of the cover plate preferably, at least partially in the same plane as the outer surface of the cover plate. The advantage of the trapezoidal form, and in particular the slightly inclined flanks, is that a V-seam which is favorable for welding can be realized. If not only the side flank of the bead is inclined but simultaneously the to be welded to cover plate has been beveled, an ideal weld preparation results.
Advantageously, the cover plates are not in back of the respective cover plate. It should be avoided that the area surrounding the cooling pipe forms an undercut, as this would be very obstructive upon removal of the cooling element. It is thus possible, within the framework of the present invention, to arrange the cover plates in parallel disposition to each other but at a sufficiently sized distance. A slightly conical disposition of the cover plates can be also contemplated. This means, that the cover plates in direction of the insertion of the cooling element are at an angle relative to each other. At least one of the cover plates is thus disposed at an angle relative to the direction of insertion. The oppositely located cover plate can be arranged parallel to the direction of insertion. At least one of the cover plates is thus disposed tilted at an angle of up to 5° relative to the direction of insertion. Preferably, an outer surface of the cover plate is at least partially in the same plane as one of the flanks of the end surface of the at least one trapezoidal bead but not in back of the end surface. The cover plates are preferably formed as level plates. It is within the framework of the present invention also possible to utilize cover plates that are curved or, at least in view of the outer surface of the cooling element, extend without an undercut so that the cooling element can be easily pulled from the melting furnace.
The process of the present invention for producing such a cooling element provides that the at least one cooling pipe is produced from a drawn hollow profile of copper or a copper alloy.
Additionally, the hollow profile can be calibrated through pressing.
Drawn hollow profiles can be produced cost effective and wherein in addition substantially any form of the bead can be realized.
It is also contemplated that in an alternative embodiment the at least one cooling pipe is produced from a bar with a cross section showing at least one bead extending along the length of the bar, wherein a channel for the cooling agent is bored along the length of the bar. While the interior hollow space in drawn hollow profiles is easier to produce than through boring, the boring is carried out with great precision on relatively soft copper materials with high forward feed at high speed. Thereafter, the lengthwise bored bars or drawn hollow profiles are bent into the desired shape.
The welding of the at least one cooling pipe together with the cover plate can be carried through a process of arc-welding. Likewise, friction welding is a suitable process to connect the cover plate with the at least one cooling pipe. In addition, electron-beam welding can be applied.
The cover plate can be welded between the beads of adjacent sections of the cooling pipe depending on the welding process. It is also contemplated that several cooling pipes that are extending substantially parallel to each other, to weld the cover plate with only one bead of the outer cooling pipe spanning an inner cooling pipe adjacent to the outer cooling pipe.
The empty space between the cover plates opposite each other can be filled with a mass of fireproof material.
The substantial advantage of the present invention is that the cover plates are welded together with the beads without the welding process, respectively, the thermal impact zone accompanying the welding process weakening the structure in the area of the wall thickness of the pipe. A further advantage is that the cover plates are also being directly cooled via the resulting welding seams.